[PATCH v2 6/9] iomap: Convert read_count to read_bytes_pending

[Matthew Wilcox (Oracle)]

Instead of counting bio segments, count the number of bytes submitted.
This insulates us from the block layer's definition of what a 'same page'
is, which is not necessarily clear once THPs are involved.

Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
---
 fs/iomap/buffered-io.c | 41 ++++++++++++-----------------------------
 1 file changed, 12 insertions(+), 29 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 9670c096b83e..1cf976a8e55c 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -26,7 +26,7 @@
  * to track sub-page uptodate status and I/O completions.
  */
 struct iomap_page {
-       atomic_t                read_count;
+       atomic_t                read_bytes_pending;
        atomic_t                write_count;
        spinlock_t              uptodate_lock;
        unsigned long           uptodate[];
@@ -72,7 +72,7 @@ iomap_page_release(struct page *page)
 
        if (!iop)
                return;
-       WARN_ON_ONCE(atomic_read(&iop->read_count));
+       WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
        WARN_ON_ONCE(atomic_read(&iop->write_count));
        WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
                        PageUptodate(page));
@@ -167,13 +167,6 @@ iomap_set_range_uptodate(struct page *page, unsigned off, 
unsigned len)
                SetPageUptodate(page);
 }
 
-static void
-iomap_read_finish(struct iomap_page *iop, struct page *page)
-{
-       if (!iop || atomic_dec_and_test(&iop->read_count))
-               unlock_page(page);
-}
-
 static void
 iomap_read_page_end_io(struct bio_vec *bvec, int error)
 {
@@ -187,7 +180,8 @@ iomap_read_page_end_io(struct bio_vec *bvec, int error)
                iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
        }
 
-       iomap_read_finish(iop, page);
+       if (!iop || atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending))
+               unlock_page(page);
 }
 
 static void
@@ -267,30 +261,19 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, 
loff_t length, void *data,
        }
 
        ctx->cur_page_in_bio = true;
+       if (iop)
+               atomic_add(plen, &iop->read_bytes_pending);
 
-       /*
-        * Try to merge into a previous segment if we can.
-        */
+       /* Try to merge into a previous segment if we can */
        sector = iomap_sector(iomap, pos);
-       if (ctx->bio && bio_end_sector(ctx->bio) == sector)
+       if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
+               if (__bio_try_merge_page(ctx->bio, page, plen, poff,
+                               &same_page))
+                       goto done;
                is_contig = true;
-
-       if (is_contig &&
-           __bio_try_merge_page(ctx->bio, page, plen, poff, &same_page)) {
-               if (!same_page && iop)
-                       atomic_inc(&iop->read_count);
-               goto done;
        }
 
-       /*
-        * If we start a new segment we need to increase the read count, and we
-        * need to do so before submitting any previous full bio to make sure
-        * that we don't prematurely unlock the page.
-        */
-       if (iop)
-               atomic_inc(&iop->read_count);
-
-       if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
+       if (!is_contig || bio_full(ctx->bio, plen)) {
                gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
                gfp_t orig_gfp = gfp;
                int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
-- 
2.28.0